Shifting the ballast on my gaff cutter

[tomdmx]

Working hard on getting my gaff cutter sorted out so aim to have her in the water in April are become more realistic as the days go by...

Right now I thinking of moving the ballast to the bottom of the keel...her original design was ballast in bilge (sand/stone bags) which I can replicate but thinking about design etc, a person whom I always think of very knowledge in this space suggested that a rail beam (or similar) of about 300kg is fixed to the bottom of the keel..

So I wanted to hear opinions on what is the impact of this...in my limited view it makes sense as you shift the weight down therefore making her more stable and less? suspectible to knockdowns etc?

 

[Wansworth]

Putting the weight that you carry as internal ballast on the bottom of the keel will increase the pendulum effect of the keel so the boatmayroll more downwind or at anchour.Extraleverage could strain construction.Loose ballastis sometimes useful to lighten ship in an emmergency.

 

[tomdmx]

I knew it wasnt as simple as that and that better men than I surely thought about this before currently the ballast lays about 2/3 up the keel so just below the waterline which is the original design...

 

[BAtoo]

If I understand you right this chap means to fix a piece of rail to the bottom of the keel -nonsense indeed. Pendulum effect wrong, hull not designed to carry it, snagging, aerodynamics - all wrong.......

 

[tomdmx]

No probs...will stick to the original plan on that point it was hessian bags filled with stones which was thrown away...so do I need to get stones again or is cement an ok substitute (or what else can be used?)

 

[dancrane]

Enjoy the silence?

Hello Tom. Very interested to read of your work on the gaffer. What tonnage/vintage is she? Any photos?

Be warned, I'm not known for my practical or proven ideas...so...

...last year, I was thinking that a dozen or more chunky deep-cycle batteries could propel a ten-meter yacht, via a couple of those clever Italian 'Agni' electric motors. And the diesel donkey could be left on the dock with its burdensome, space-wasting fuel tank.

The main discouragement wasn't that the amps wouldn't last more than a few short hours - I'm happy to regard sailing as not intrinsically about getting anywhere fast - and I daresay as a gaff rig fan, you're likewise more interested in the pure peace of sailing, than hurrying about under auxilliary power.

No; the problem with an electric motor was where to put all the batteries? And in modern designs, the question has no answer.

But the cavernous bilges of an old-school long-keeler, would provide space...and the huge weight of the batteries (properly insulated), could substitute for the concrete, scrap metal or other weighty stuff, parked in the bilge by the original builder.

I only mention it, because if you're pulling the ballast out anyway, why not replace it with a few grands' worth of Exide's finest? (And say farewell to most of the diesel downsides that afflict half the questioners/contributors here!)

I recognise it's not for everyone - or perhaps, anyone - interesting idea, though. To me...

(Before I'm attacked by fleets of objectors reminding me that batteries need too much charge, let me say I was thinking of a hybrid arrangement... employing a compact internal combustion generator as back up for the wind-gens, solar panels, shore power, etc...)

 

[Deleted member 36384]

No probs...will stick to the original plan on that point it was hessian bags filled with stones which was thrown away...so do I need to get stones again or is cement an ok substitute (or what else can be used?)

There are ways of casting concrete using the frames as formers such that the concrete ballast sits in the allocated space securely, allows the air to circulate around and more importantly can be easily removed. Filling the space with concrete applied straight onto the wood is not a good idea. Lead can be cast into ingots and similarly fastened in place between the frames.

For example: place thin ply around the area that you wish have concrete, line with plastic, use expanded mesh to fill the space following the shape, attach a couple of steel hoops to the expanded mesh which will protrude out the top of the poured concrete, using a thick mix, trowel in the concrete forcing well into corners such that it is just under half the depth, insert the expanded mesh, trowel in the reminder of the concrete and tamp down well.

Once set remove the ballast and discard the ply, insert ply spacers, to hold the concrete off the hull, strap in place. Apparently iron and lead has also been cast into the concrete (or cement) to increase the mass of the ballast. This is a recollection from a repair book I have. If I can find it I shall quote the book here.

 

[Simondjuk]

...aerodynamics - all wrong.......

If the aerodynamics of the keel are being explored, something really is all wrong!

 

[William_H]

Ballast

The ballast in the hull will contribute to the stiffness of the boat. That is it's ability to stand up in a strong wind. Ballast on the keel tip will do the same thing. Ballast on the keel tip comes into real value when the boat is knocked down. ie it contributes to self righting. Ballast under the floor does this as well but not as much leverage.
I don't think it a bad idea if you added some lead on the keel tip in the form of a shoe for deeper draft or shoes each side of the keel. ie cannoe shaped through bolted side to side. Lead is the obvious choice here. However for reasons of keel strength and possibly the pendulum effect I would not put too much lead on the keel.
If you can afford lead use it in lumps under the floor. Make them in easily handled size so you can move them or remove and replace them depending on how you find the handling.
As said concrete can also be a good ballast. Line the area with plastic then cast pieces in place again only in manageable sized pieces and ensure you can remove each lump. If you need another layer lay plastic sheeting over the first lumps to separate the pieces. good luck olewill

 

[westernman]

I have a 13 ton chunk of lead outside in the middle of the keel of my gaff cutter. However it was designed from the start with that arrangement in mind.

As far as putting concrete directly on top of wood goes - this is the way it used to be done back at the end of the 19th century. People who have had boats from that period tell me that when renovating, they find that the wood underneath that concrete is better preserved than anywhere else. There may be some ingredient in old concrete which is a very effective rot inhibitor.

That may still be the case with modern concrete - or may be not.